<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
            width: 100px;
            height: 100px;
            background-color: pink;
        }
    </style>
</head>
<body>
    <div>1</div>
    <div>2</div>
    <div>3</div>
    <script>
        var divs = document.querySelectorAll('div')
        divs[0].onclick = function(){
            alert('1')
            divs[0].onclick = null;
            // 移除点击事件
        }
        divs[1].addEventListener('click',fn)
        
        function fn (){
            // 写在函数里 (fn)
            alert('2');
            divs[1].removeEventListener('click',fn); 
        }
        // 3
        
    </script>
</body>
</html>